Method and apparatus for mixing a fluid mass

ABSTRACT

Apparatus and method are provided for treating a fluid mass or stock, particularly couch stock in paper making. Stock material is fed into a vessel having a mixing arrangement comprising rotatably arranged processing means. At lest two processing means are caused to rotate mutually adjacent in opposite direction and essentially horizontally. The stock at the upper surface of the means is conveyed towards a wall portion of the vessel, whereby spirals arranged in an inclined manner at a core of the processing means bring stock into channels defined by the core, by the spirals, and by the wall portion of the vessel, and further towards a constriction formed by the respective spiral elements running in an intermeshed manner, while a part of the stock is forced in a direction away from a discharge of the vessel.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of application Ser. No.09/622,829, filed Sep. 26, 2000, which is the national stage under 35U.S.C. 371 of PCT/FI99/00143, filed Feb. 23, 1999, the entire contentsof which are hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a method for treating a fluidmass wherein a mass material is fed to a vessel or trough having amixing device comprising rotatably arranged processing means, wherein atleast two of the processing means are caused to rotate in oppositedirections and essentially horizontally adjacent to one another. Thepresent invention also relates to a method for treating a couch mass orthe like, wherein couch mass and dilution water are caused to fall downinto a couch pit comprising a trough and a mixing arrangement. Thus, inmore general terms the present invention relates to methods for treatinga fluid mass or stock and especially a method for treating a couch massor the or the like, wherein the mass or stock material is fed to avessel or trough having a mixing device comprising rotatably arrangedprocessing means. The present invention further relates to a processorarrangement for a fluid mass or stock, this arrangement comprising avessel or trough for receiving the respective mass or stock, aprocessing device such as a mixing arrangement arranged in the vesseland comprising horizontally arranged rotatable cylinder body meansprovided with spirals, as well as a discharge for treated or processedmass or stock. The cylinder means comprise at least two cylindersarranged for rotation counter each other. The invention further relatesto a specific use of the method and the arrangement.

BACKGROUND OF THE INVENTION

[0003] In paper manufacturing trimmed strips are cut from a wet web, andadditionally wet broke material will be generated at the wire and thepress section in connection with a web break. Usually the wet brokematerial is collected, disintegrated and diluted in a pulper comprisinga container with a powerful mixing feature and thereafter it is returnedto the process.

[0004] For the disintegration to function properly the pulper mustcomprise a sufficient amount of mass or stock which is maintained undera powerful mixing by the disintegration means of the pulper. Duringregular processing the amount of stock brought to the pulper correspondsto a minor part of a paper machine's production. At web breaks, changesof quality and machine stops the amount of stock may temporarily rise toan amount corresponding to the total production capacity of the machine.

[0005] In order to achieve a satisfactory mixing and disintegrationeffect the stock in the pulper must be kept highly diluted and asufficiently large volume of mass must be kept therein. This leads to ahigh power demand for the disintegration and mixing.

[0006] At a web break the water consumption rises greatly and for thispurpose a water reserve must be arranged corresponding to the demand ata typical web break. After the disintegration the wet broke materialusually is de-watered in a separate de-watering device for bettercorrespondence with the production consistency and for retrieving thewater therefrom.

[0007] At production changes, particularly when the color is changed,there exists a large amount of wet broke material from the earlier paperrun, which cannot be used for the next paper run. The wet broke materialin circulation in the system also slows down progress in attaining thenew paper quality, resulting in production losses and change-over brokemasses.

[0008] It is also important that the pulper be easily and completelyemptied of its contents, which is not the case for typical pulpers.

[0009] Many paper machines have a low and narrow wire section which doesnot provide space for constructing an appropriate pulper. In this case,vaulting and broke stocking problems will arise, and the pulper itselfcan be difficult to maintain and service.

[0010] Corresponding problems occur in other productions in which a massor different streams of components are to be processed in order toachieve a homogeneous mass.

[0011] Usually the wet broke mass is diluted to a 2 to 3 percentconsistency in a couch pit or wire pulper. Depending upon the structureof the paper machine, a similar pulper may also be arranged inconnection with the press section. Depending upon the size of themachine, the wire pulper is typically between five and fifty cubicmeters, and it comprises a powerful mixer which breaks up fiber bundlesand pieces of paper. In order to function effectively, the pulperrequires good mixing which, in turn, requires a sufficient dilution ofthe mass. Since the pulper works under a variety of conditions, thedilution usually is over-dimensioned according to the most criticalsituation.

DESCRIPTION OF RELATED ART

[0012] Publication No. SE-210862 describes a device for processing amaterial mass in particulate or suspension form, especially forde-fibration of a cellulose material, in which device at least two bandspirals are arranged mutually adjacent in a shell having inlet andoutlet openings, said spirals being arranged for spaced intermeshedcommon rotation. Their spiral surfaces are directed generally radially.

[0013] Since the device known from SE-210862 has defined inlet andoutlet openings and a mainly unbroken axial path of flow it isunsuitable for processing a broke mass which will fall down over thewhole width of a paper machine. The axial spiral surfaces give aprocessing of the mass in an axial direction, and the mixing of the masswhich takes place does so because the band spirals will cut through themass, which provides only a local turbulence and permits the mass tostagnate within the device. A clearance between the band spirals andsaid shell has also been provided in order to permit this kind ofmixing, and separate screws take care of the feeding of the mass throughsaid outlet.

[0014] U.S. Pat. No. 2,797,623 discloses a worm conveyor by which brokemass can be transported out from a paper machine. The worm conveyorcomprises a screw in which the broke in a traditional manner is broughtalong a flute. For this transport to function the spiral surfaces of thescrew must be arranged essentially radially. Broke falling into theconveyor will thereby be transported straight through the conveyorwithout any significant mixing.

[0015] Publication No. DE-401033 discloses a mixing and transportarrangement having two intermeshed band spirals. Since they are rotatingagainst each other, the material transported by them will be processedin an alternating manner by one or the other of the spirals and therebya mixing action will be generated. This mixing action thus comprises thespirals moving through the material to be mixed and simultaneouslytransporting it forwards. A mixing in this kind of agitator requires aneasy flowing material and there is a risk, if the screws fill up, for astanding circulation to be caused, since the material can easily flowthrough hollow portions in the spirals.

[0016] Especially in small old paper machines the agitator in the couchpit has been formed as a spiral, with the idea of its pressing the brokematerial towards the outlet of the couch pit. These spirals, however,have been inefficient in that they have not ground up the broke and havenot provided a sufficient power, and thus the broke has been able tovault and block the outlet.

[0017] The broke is usually transported from the pulper via a thickenerto the machine's stock chest where it is mixed with fresh stock. Thiscan be arranged in many ways, depending upon the machine's product andequipment. It is usual to combine the thickening of the broke with fiberrecovery in a disk or drum filter.

[0018] At a change of quality the broke can be directed to separatecollecting tanks from which it is gradually dosed into the stock. Inmany cases, especially in the manufacturing of colored paper, the brokegenerated at a change of quality can no longer be added to the processbut will be directed to the waste water treatment where the solidmaterial is recovered for incineration or deposition on a waste dump.

[0019] Usually the generated broke will be struck from the wire by highpressure water which simultaneously dilutes the broke. There have,however, been developed methods for mechanically dislocating broke, onemethod used including feeding it over a guiding roll having a doctorblade. Hereby the desire has been to avoid an unnecessary dilution ofthe broke. There is, however, the problem that broke of a higherconsistency tends to vault, which is accentuated by a more difficultmixing.

SUMMARY OF THE INVENTION

[0020] It is an object of the present invention to provide a method andapparatus for an efficient, continuous homogenization of a mass flow,such as a wet broke in a paper machine or another fluid mass comprisingmore or less solid components which are to be disintegrated and/or mixedinto a liquid type fluid.

[0021] Another object of the present invention is to provide a methodfor handling, for example, wet broke of high consistency, so that theneed for adding diluting water and subsequent thickening is eliminated.

[0022] A further object of the invention is to provide a vaulting andblocking free handling of, for example, broke, also in narrow spaces.

[0023] A further object of the invention is to provide an energy savingmethod for handling of, for example, wet broke.

[0024] One object of the invention is to provide an apparatus capable oftreating, for example, wet broke in a small volume and one which permitsa simple and complete emptying of the same.

[0025] One object of the invention is also to provide an apparatuscapable of treating, for example, broke of a high and varyingconsistency.

[0026] One further object of the invention is to provide an apparatus ofsmall dimensions which also in narrow spaces is capable of treating, forexample, broke without a risk for vaulting and blocking.

[0027] One further object of the invention is to provide an apparatuswhich under a low energy consumption treats, for example, broke.

[0028] According to the invention the set objects are obtained byarranging, in a vessel, a system comprising spiral means operatingcounter to each other and in an intermeshing fashion in such a mannerthat the mass at the vessel's wall will reside in channels formed bysaid spirals, whereby the mass at the intermesh of said spirals will bepressed into a direction which differs from the traditional directionsof transportation for the spirals.

[0029] Thus, the method according to the present invention ischaracterized in that at least two of the corresponding means arebrought to rotate in opposite directions and essentially horizontallyadjacent to one another so that the mass at the upper surface of themeans is conveyed outwards towards the respective opposite side walls ofsaid vessel, whereby the mass is brought, by several spiral elementsarranged in an inclined manner at an essentially cylindrical core of therespective processing means, into generally inclined channels delimitedby the core, by the walls at respective two adjacent spiral elements,and by the vessel's wall portions adjacent to the respective spiralelement, and further towards a constriction or choke formed by therespective intermeshing spiral elements at adjacent processing means.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 shows a processing arrangement according to the invention,which arrangement is used as a couch pit in a paper machine,corresponding to section II-II in FIG. 2.

[0031]FIG. 2 shows a corresponding processing arrangement seen fromabove.

[0032]FIG. 3 shows an embodiment of the processing arrangement havingten spirals arranged on each spiral cylinder, corresponding to sectionI-I in FIG. 1.

[0033]FIGS. 4a and 4 b show corresponding sections in some otherembodiments of the processing arrangement.

[0034]FIG. 5 shows a section of a couch pit having a central outlet.

[0035]FIGS. 6a and 6 b show a processing arrangement having two pairs ofspiral cylinders, seem from above and, respectively, in section III-III.

[0036]FIG. 7 schematically shows the use of the processing arrangementas a couch pit in a paper machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.

[0037] Favorably the method comprises bringing a part of said mass to bepressed against at least one outlet arranged in the vessel, bycontrolling the spiral elements' rotation and pitch around the coreand/or the vessel's inlet and/or outlet parameters, the rest of saidmass being pressed, suitably under the impact of at least one gable endof said vessel and/or the impact of the spirals acting in an intermeshedmanner, through the channels and into a direction away from the outletand/or up over the upper surface of the processing means to join themass being fed into the process.

[0038] A method according to another embodiment of the invention,especially arranged for treatment of couch mass, is characterized bybringing at least two essentially vertically arranged spiral cylindersof said mixing arrangement to rotate in an intermeshed manner counter toeach other so that mass dropping down will be transported by saidspirals outwards against the respective outer sides of the couch pit,where the mass is drawn in into channels formed by adjacent spirals, bythe respective core bodies of the cylinders and by a wall of the troughso that the mass will be conveyed towards a constriction formed by thecylinder cores and the mutual intermesh of said spirals, whereby aportion of the mass will be pressed towards an outlet, a portion of themass will circulate in channels formed at the constriction, and surplusmass will be pressed backwards through said channels.

[0039] According to a preferred embodiment of the method the amount ofdilution water is controlled according to the width of the down-fallingpaper web constituting the couch mass, suitably to obtain a consistencycorresponding to the consistency of the fresh stock in a papermanufacturing process and suitably so that the stock is returned to amass processor without a preceding thickening. Hereby the returnedamount is suitably restricted to a pre-defined proportion of the totalstock while any surplus amount suitably will be fed to a collecting tankand/or so that, at a change in the paper machine, the level in said thepit is restricted to a minimum by controlling the rotation of the spiralcylinders, by choking the outlet or in another way.

[0040] The arrangement according to the invention is especiallycharacterized in that the cylinder means comprises at least twocylinders arranged for rotation counter to each other, respective spiralmeans extending directly from the surface of each respective cylindercore to the vicinity of a respective wall section of said vessel, saidcylinders being arranged so that the spiral means at least in pairsintermesh to define generally inclined horizontal channels having asmaller cross section than those channels which at each respectivecylinder are formed between adjacent spirals, the cylinder core and awall section of the vessel.

[0041] The direction of rotation for each respective cylinder issuitably such that the mass at least at the outermost cylinders ispressed by the spiral means against the side walls of the vessel anddownwards along them towards a favorably respective semi-circularportion of the vessel and suitably towards the vessel's outlet and,respectively, towards the vessel's gable walls. The dimensions of theinlet and outlet, respectively, are suitably such that the mass, due tothe rotation of the spiral means, is at least partially pressed throughthe channels in a direction away from the outlet, the system of spiralssuitably being so tight that a pressure will be built up in front of theoutlet.

[0042] According to a favorable embodiment of the invention eachrespective spiral cylinder comprises a core suitably in the shape of adisplacement body having a considerable diameter in relation to thetotal diameter of the spiral cylinder. The diameter of the body issuitably at least 50 percent, preferably about 75 to 95 percent of thetotal diameter. The number of spirals on each cylinder is suitably morethan one, preferably 4 to 40, where the spirals are arranged in such amanner that their pitch suitably is more than three diameters per turn,the angle (α) between the outer edge of a spiral and the normal planeperpendicular to the axis of said cylinder then being more than 45° C.This angle ay is preferably more than 60°, preferably about 65° to 85°.The spiral means are suitably arranged around each respective cylindercore along essentially the entire horizontal extent thereof.

[0043] According to a preferred embodiment the pitch of the spirals issuch that the pitch corresponds to the length of the cylinder on about ½to 1 turn. Thus the channels formed by the spirals will run from theinlet end of the arrangement almost to the outlet end thereof, and incertain cases, the whole way. The spirals according to the invention mayin this preferred embodiment be defined as several parallel screwsarranged on a common core, and here it should be noted that thesespirals, in contrast to arrangements shown in the prior art, have such ashape and pitch that the processed material in practice cannot keep upwith the spiral pitch, and that the spirals are not, at first hand, usedfor transportation of material but for mixing. The spirals do notnormally gear into each other in a mutual contact, but instead aneffective mixing action is achieved by pressing the material between thespirals and in the form of a leaking between the spiral edges and thevessel's walls.

[0044] According to an alternative embodiment the shape of the spiralsis such that the spirals comprise a triangular, or in another manner,essentially two-dimensional cross section, while the embodimentdisclosed in the appended figures comprises essentially blade-likestructures. The dimensioning and individual structure of the spirals issuitably adapted according to the material to be processed, so that thespirals at the rotation do not to any essential degree bring air withthem, while simultaneously the material to be processed has time to flowin between the spirals.

[0045] According to one embodiment of the invention the spiral cylindersare arranged in pairs and are rotatable so that the cylinders at theouter sides thereof, which sides are directed towards the vessel's wall,together with said wall or, respectively, at the area between anypossibly existing adjacent other pairs of cylinders form a nip orwedge-shaped inlets for the mass, suitably so that each respective nipor wedge-shaped portion comprises a shearing/cutting edge portionco-acting with the spiral edge. According to another embodiment morethan two spiral cylinders are arranged to interact suitably in pairs.

[0046] In the figures different embodiments are shown in which thenumber of outlets varies. According to one embodiment, the number ofoutlets is greater than one, whereby the spiral cylinders suitably aredivided in sections, each leading to a respective outlet. According toanother embodiment, the outlet is centrally located. The spiralcylinders then suitably being divided in sections, each leading towardthe center. According to another embodiment, each respective outlet iscentrally located between the cylinders of the respective interactingpair of cylinders.

[0047] According to the present invention a flow or flows to behomogenized are processed so that they are conveyed to a vessel ortrough, on the bottom of which spiral shaped sets formed as intermeshingspiral cylinders rotate and feed the mass towards one or more outletopenings. The spiral cylinders, consisting of a cylindrical core andspirals closely attached thereto, are brought to rotate so that theirupper sides move away from each other, whereby the mass will be conveyedthe outer way around the spiral cylinders towards their undersides. Herethe intermeshing of the spirals forms a choke portion which partiallyprevents the mass from following the rotation of the spiral cylinder,and thus the mass will be pressed, by the spiral movement of the spiral,towards an outlet located under the spiral cylinders at their end.

[0048] The direction into which the mass is pressed by the rotatingspiral is the spiral's pitch direction, the spiral pitch being thedistance between the spiral turns in the axial direction of the spiralcylinder. The higher the pitch the more acute the spiral angel will be,which angle is formed between the outer edges of the spirals and anormal plane imagined with respect to the axis of the spiral cylinder.

[0049] Traditional spiral conveyors usually have a pitch correspondingto one spiral diameter or less for each turn. In such a case the spiralangle will be 17.5° C. or less, the action of the spiral being, aboveall, forwarding in the direction of the axis, the mixing impact beinginsignificant. According to the present invention a mixing action isachieved by pressing the mass against a constriction between thecylinders and thus the mass is forced to flow through the channelsformed by the spirals and the core or the vessel, and especially in adirection opposite to the spiral's aforesaid forwarding direction. Inorder to intensify this impact the spirals are suitably given a higherpitch so that the spiral angle α is 45° or suitably even more,corresponding to a pitch of about 3 times the spiral diameter or more.An especially good efficiency is achieved for spiral angles of 60° ormore, corresponding to a pitch of 5.5 times the spiral diameter or more.

[0050] If one wishes to have more than one outlet the spiral cylindersare divided into sections having different pitch angles, so that masswill be conveyed to each of said outlets. Such outlets may be arrangedat both ends of the spiral cylinders, or centrally. For centrallyarranged outlets, the spiral sections are favorably chosen so that thepitch of the spiral sections meet at the outlet, which thus will be fedfrom two directions.

[0051] By utilizing multiple spirals, multiple flow channels areachieved. By letting the outer edge of the spirals extend into the nearvicinity of the core of an adjacent spiral cylinder, the accessiblevolume for each unit of angle at the meshing point of the spirals willbe half of the same in their free portion. Simultaneously, a labyrinthis achieved which prevents the mass from leaving the flow channels, andthus any surplus mass not received by the outlet will be forced to flowbackwards along the channels in a direction which, thus, will beopposite to the direction in which the spirals at an open rotation wouldconvey the mass.

[0052] The sides and/or bottom of the vessel or trough are suitablyshaped into a form which rather closely follows, at least for a part ofthe circumference, the periphery of the spiral cylinders. The trougharound the spirals is favorably shaped to have semi-cylindrical bottomsections so that the outer edge of the spirals adjacent to the outletwill pass closely near the trough in a sector corresponding to at leastthe distance between two spirals. Correspondingly, the spiral endsfavorably are arranged so that they pass near the trough gable. Thus, atleast one spiral at each side will press mass towards the outlet.

[0053] Since only a portion of the mass can rotate along with thespirals, that portion of the rest of the mass which is not conveyedtowards the outlet openings will be forced into an opposite directionalong channels formed by the spirals. The flow of mass will beaccelerated and shearing forces will appear in the mass. These shearingforces contribute to the disintegration of, for example, fiber bundlesand sheets of paper or other conglomerates of components of the mass tobe processed, which components usually are more consistent in relationto the dilution fluid. Simultaneously, this partial flow directedcounter to the main flow of the mass will contribute to an effectivemixing and equalization of the mass composition.

[0054] To that part where the channels between the spirals are notclosed by the semi-cylindrical sections of the trough, the surplus masswill be forced forwards along the channel and up in the trough, whichfurther makes the mixing in the trough more efficient. By designing saidsemi-circular sections to cover a greater or lesser portion one canaffect the portion of mass being forced backwards through saidconstriction or, respectively, forwards through the open channels.

[0055] If the transition between semi-cylindrical section and the sidewalls of the trough is made sharp the spirals will, at their rotationbeyond this edge, shear off larger pieces of mass located near thisedge. This facilitates the treatment of a mass comprising largercontinuous sheets, which for instance may be the case for a papermachine where the couch mass has passed through a press.

[0056] Since it is desirable to have only a small amount of mass undertreatment, it is preferred to design the core of the spiral cylinders asa displacement body having a relatively large diameter, preferably atleast half the spiral diameter. Especially favorably the core diametermay be about ¾ of the spiral diameter or more.

[0057] The larger the spiral pitch, the higher number of spirals thespiral cylinders should comprise in order to achieve the desired channeleffect. When the number of spirals is chosen, it should be taken intoconsideration that the distance between the spirals should be selectedin relation to the viscosity of the mass and the rotational speed of thespiral cylinders, so that the mass initially will have the time to fillthe channels prior to reaching the semi-cylindrical portion of thetrough. Typical combinations for the couch mass in a paper machineshould be: Spiral diameter Core diameter Pitch at each Number of spiralsmm mm Turn, mm on the cylinder 600 300 2000 6 800 600 4000 16 1000 9006000 40

[0058] For the homogenization of other media the dimensions mayconsiderably differ from the above. For instance, for producingcosmetics, much smaller dimensions would be considered.

[0059] In the embodiments disclosed in the figures the spirals, as such,are relatively thin, but according to a special embodiment of theinvention the spirals are made of displacing spirals having a tight fit,suitably so that adjacent spirals acting in an intermeshed manner to aconsiderable extent, suitably to 50 to 98 percent, fill up the voidspace between the cylinder cores. By such an arrangement an especiallyefficient mixing can be achieved, since the spirals constitutedisplacement bodies which totally or partially fill the channels in theconstriction between the spiral cylinders. The thus achieved choke orpartial choke of the re-flow through the channels in the constrictionraises the pressure towards the outlet and bring about an especiallyforceful processing of the mass which leaks through the channels and thenarrow slits between the spirals and the through.

[0060] This corresponds to the action of pumping with screw pumps havinga positive choke, and it can be utilized for feeding the mass forwardsthrough the outlet without separate pumps.

[0061] A preferred embodiment is achieved with two spiral cylinderswhich are partially surrounded by a semi-cylindrical section of thetrough bottom and side, the spiral cylinders rotating away from eachother, viewed from above, so that the treated mass will be pulledoutside of the pair of spiral cylinders towards the semi-cylindricalsection and further in towards the nip formed where the spiralsintermesh.

[0062] The spiral cylinders are made so that the gap between them isnarrow. Preferably this can be achieved by utilizing multiple spiralsand further by providing the spiral cylinders with a cylindrical core.Thus a labyrinth is achieved which prevents the mass from circulatingalong with the cylinders.

[0063] Most preferably the bottom of the trough is designed assemi-cylinders following the shape of the spiral cylinders and having atangential transition to the trough side, thus constituting a wedge-likeinlet. Hereby there is achieved a maximally efficient mass introductionand the volume of the trough is minimized. At the same time, theemptying is made easier since the spiral cylinder will pass over thetrough bottom in its close vicinity. Alternatively, the transition tothe trough side can favorably be designed as a sharp edge which togetherwith the spirals constitutes a shearing tool.

[0064] In order to facilitate the emptying it is preferred to providethe trough bottom and the spiral cylinders with a slight inclinationtowards the outlet opening. A favorable inclination is of the order of 1to 5 percent. A corresponding effect can also be achieved by making thespiral cylinders and/or the spiral elements slightly conical in acorresponding manner.

[0065] The outlet opening is suitable located in one end of the trough,near the gable thereof. However, inlet opening may also, as mentioned,be located at both ends, centrally in the trough or in another desiredmanner. If the inlet openings are located elsewhere than from a locationat one end, the spiral cylinder is divided into sections having adifferent direction of the spiral turn, so that the mass is fed towardsthe outlets.

[0066] This arrangement can, as has been described above, be designedand used so that there arises a pressure towards the outlet. In order toachieve a pumping function the spirals are designed, in a manner knownto those skilled in the art, so that the gap between the spirals isclosed or minimized. Herein also the gap between spiral cylinder andtrough should be kept small, suitably only a few millimeters.

[0067] For controlling the consistency of the disintegrated mass underdifferent processing conditions, dilution water can be added, thedilution water being proportional to the portion of total web widthwhich is conveyed to the couch pit. Thus, the consistency of the couchmass can be controlled to approximately correspond to the consistency ofthe fresh stock fed into the process.

[0068] The mass can also be treated by more than two spiral cylinders,in which case it is favorable to arrange the spiral cylinders in pairsso that each pair of spiral cylinders function as described above.Hereby it is preferred to arrange the pairs of spiral cylinders so thatthey together form a suction nip which draws a mass in between thespiral cylinders. If for several spiral cylinders a relatively highpressure level is desired, outlet openings should be arranged separatelyfor each pair of spiral cylinders.

[0069] By the invention a compact system is achieved for treating, forinstance, a broke mass of high consistency obtained in manufacturing ofpaper. Hereby it will be possible to bring the mass directly from thebroke pit back to the process, whereby any delays in the qualityadaptation can be avoided. Especially favorably this can be performedthrough a stock preparation according to patent applicationPCT/FI96/00052 by the same inventor.

[0070] In cases where the shredding and disintegration of a fiber bundleis especially critical, the invention can be combined with a de-stripperfor treating the outgoing flow.

[0071] This is illustrated by the following example. If two spiralcylinders with a diameter of 600 millimeters having a core diameter of300 millimeters rotate one turn a second, the circulation in the spiralcylinders would be totally 563 liters/second for each meter of machinewidth. At a web break the production of the paper machine, 10tons/hours, corresponding to a net flow of 70 liters/second at aconsistency of 4 percent, will be discharged towards the outlet in thepressure direction of the spirals. The circulation is 493 liters/secondor 7 times larger than the net flow for each meter of width. This willflow along the channels, which provides good mixing efficiency.

[0072]FIG. 1 discloses a couch pit embodiment comprising a vessel ortrough 10 having a discharge 12 at one gable end 16 and a spiralcylinder 20 located near a suitably semi-cylindrical portion, i.e., thebottom 11 of the trough 10. Sheets 30 of mass from trimmings from apaper machine fall down into the couch pit where they are collected inthe form of a mass generally indicated by reference 32.

[0073]FIG. 2 discloses a section I-I of the couch pit according to FIG.1 and an arrangement of two spiral cylinders 20, 20′, each of whichhaving a core 22 and 22′, respectively, and six spirals 24, 24′ arrangedso that the spirals of the cylinders in the area between the cores 22,22′ intermesh, preferably so that an outer edge of said spiralcylinder's 20 respective spirals 24 will be close to the spiralcylinder's 20′ core 22′, whereby a gap 28 is formed as disclosed in FIG.3. The shortest distance between the cores 22, 22′ constitutes aconstriction 26 where said spirals 24, 24′ and, respectively, 24″interlace in mutual interdigitation.

[0074] The number of spirals 24, 24′ and 24″ may be higher or lower thansix for each spiral cylinder. Even though the invention functions withone single spiral on each spiral cylinder, six spirals usually is themost favorable, since these are needed to provide a more efficientlabyrinth in the constriction 26. If the spiral cylinder, as disclosedin FIG. 4b, is designed to have a relatively larger core, the number ofspirals should be higher, preferably up to forty or more, depending onthe relationship between the diameters of the spiral and the core.

[0075] The spirals 24, 24′, 24″ and the cores 22, 22′ form, betweenthemselves, channels 35, 35′, and together with the semicircular portion11 of the trough, channels 34. Reference numeral 33 indicates suchchannels which at least partially comprise portions which are locatedoutside the trough's 10 suitably semicircular portion 11 whichessentially closely fits against said spirals 24, 24′, 24″. Gables 16,16′ are preferably arranged so that the gap between the gables 16, 16′and the spiral cylinders 20, 20′ is small, whereby the channelsindicated by reference numeral 34 at their ends will be essentiallyclosed by said gables 16, 16′. Thus, the mass conveyed by the spiralstowards the nip 25 will have its only outlet through the discharge 12 orthe channels 35, 35′. At the end opposite to the discharges the channels34 will be in direct contact with such channels 33 which are at leastpartially open and thus allow a flow mainly over the top of thecylinders 20, 20′ and in a direction counter to the rotational directionof the spiral cylinder in a direction towards the discharge 12. Here itis to be observed that reference numerals 33, 34 and 35 indicate arelative partition of the channels in accordance with a certain propertyand in a position disclosed in the respective Figure, and that theproperties of each specific channel with respect to openness andconstriction will change as the relative positions of the respectivechannel changes due to the rotation of the cylinder 20.

[0076] Seen from above the spiral cylinders 20, 20′ rotate outwards,whereby any mass 32 in the channels 22 will be drawn, due to therotation of each respective spiral cylinder, towards thesemi-cylindrical portion 11 of the trough and into channels 34 andfurther to an inner nip 25 where the spirals 24, 24′, 24″ intermesh, andfurther towards the constriction 26. Due to the spiral movement of thecylinders the mass 32 will be conveyed preferably towards the dischargeend of the couch pit 10, at which end the level of the mass 32 will riseso that a return flow 36 is formed. In the channels referred to as 34,34′ closest to the gable 16, the gable will prevent the mass 32 fromflowing forwards, and thus surplus mass will flow backwards instead aschannel flows 38 along channels referred to as 35, 35′ through theconstriction 26. After having passed the constriction 26 the speed ofthe mass will slow down so that the mass flow will fill up the channels.Hereby the return flow 36 at the surface of the mass 32 will be conveyedover the channel flow 38 which among others contributes to preventingmass sheets 32 from being drawn directly to the discharge 12 prior totheir being subjected to a sufficient mixing and shredding at the spiralcylinders 20, 20′.

[0077] To that part where the channels 34 are not shut by said gable 16the mass 32 which does not follow the rotation of the spiral cylinderswill favorably be forced forwards along the channels 34 towards thedischarge end to the open channels 33 and will again be drawn towardsthe constriction 26. If the volume of the spiral structure itself isrelatively small and frictional losses are discounted the portion ofmass flowing forwards would be ⅔ in the present case, while the portionflowing backwards would be ⅓ of the total amount of mass circulating. Ifthe spirals displace more volume, the amount of mass flowing forwardscorrespondingly increases.

[0078] During operation trimmings from the paper machine will fall assheets 30 of paper mass down into said trough 10, whereby they areconveyed by the rotating spiral cylinders 20, 20′ towards a nip 37 atthe transition between the sides 14 of the trough 10 and its bottom 11and onwards towards the constriction 26 between the spiral cylinders 20,20′. When a sufficient amount of mass has been gathered in the trough10, the space between said spirals 24, 24′, 24″ at the spiral cylinders20, 20′ will be filled with mass 32. Due to the rotation such mass whichis located in the channels 33, 34 of the spirals will be conveyedtowards the constriction 26 whereby the available channel volume betweenthe spirals 24, 24′, 24″ will be reduced to about one half.

[0079]FIG. 2 discloses a pair of spiral cylinders 20, 20′ seen fromabove and shows how spirals 24, 24′ having opposite rotationaldirections intermesh. When a spiral cylinder is chosen one should takeinto consideration to leave a sufficiently large free surface betweenthe spirals so that the broke actually falls into said channels 33between the spirals and thus can be drawn with them into the channels34.

[0080]FIGS. 4a and 4 b disclose other embodiments of, e.g., a couch pitdesigned in accordance with the invention, the pit being designed tohave an increased height. In FIG. 4a the spiral cylinders comprise tenspirals, in FIG. 4b twenty spirals each. The higher couch pits contain abuffer capacity for broke mass and they can be operated according to thesame principles as conventional couch pits, i.e. with a level controland variable discharge pumping. Especially FIG. 4a shows how thetransition between the side 14 and the semi-cylindrical bottom 11 of thetrough 10 is designed to have a sharp edge against which said spirals 24can cut sheets of mass. The embodiment according to FIG. 4b isespecially favorable since the high volume cores 22, 22′ will displacemass, whereby the amount of mass in the treatment arrangement is keptsmall.

[0081]FIG. 5 shows, as an example, a couch pit having a centraldischarge. The spirals 24 are designed to have two sections 120, 120′having different turning directions so that they force the mass towardsa centrally located discharge 12′. The Figure shows the situation duringa web broke when in addition to trimmings 30 also broke 31 will fallinto the couch pit which is loaded over its whole width. In a breaksituation the flow through the couch pit will increase to a multiple ofnormal operation. Then it may be favorable also to increase therotational speed of the spiral cylinders and thereby also theirshredding and pumping efficiency. For this reason they are preferablyprovided with a driving device having a variable rotation. Forcontrolling the operation of the arrangement it may also be preferableto provide each respective discharge, and in some cases also eachrespective inlet, with choke means (not shown), thus facilitating thecontrol of the essential operative parameters of the arrangement.

[0082] Since the removal of mass through the discharge is less than theconveyor capacity of the spiral cylinders 20, 20′, the mass 32 will bepressed through the constriction 26 and the gaps at the spiralcylinders, which brings about a collection of mass on top of the spiralcylinders. Also on the upper side the spiral cylinders will convey mass32 generally towards the location of the discharge 12 which will bringabout a level rise there and further to a recirculation of the surfacemass, which causes broke and trimmings to be conveyed especially awayfrom said discharge prior to their being drawn into the channels 34.Thereby they will pass through a large portion of the spiral whichenhances the probability that fiber bundles and lumps of mass will besubjected to shredding and thus disintegrated. The same effect can alsobe seen in FIG. 1, even though the falling mass here is conveyed towardsone end of the trough.

[0083] In cases where a broad couch pit is needed it is preferred to usemore than two spiral cylinders, as disclosed in FIGS. 6a and 6 b. Inthis case four cylinders have been arranged. It is favorable to arrangethe spiral cylinders in pairs 45, 45′ so that the nip 27 which is formedbetween the most central cylinders and where said cylinders draw massdownwards is made so broad that it does not prevent the movement of themass in the same manner as constrictions 26 in the upwards leading nips.When several pairs 45, 45′ of cylinders are applied it is favorable toarrange separate discharges 12″ for each pair of cylinders, whereby thepairs 45, 45′ of cylinders can build up a pressure in front of therespective discharge 12″ and effectively convey the mass 32 towards it.

[0084]FIG. 7 discloses a preferred use of a processing arrangementaccording to the invention as a couch pit in connection with a papermaking process where the paper machine is supplied with mass from acompact stock preparation 50 according to patent applicationPCT/FI96/00052 by the same inventor. Stock is pumped to the shortcirculation of the machine by a stock pump 51, which is controlled sothat the dry flow of stock over a sensor 52 is kept at a desired level.The stock is diluted in a conventional manner in a mixer pump 53 and fedover a cyclone cleaner 55 and a screen 57 to the headbox 59 and a wiresection 61. Backwater draining from the wire section is distributed intopartial flows in accordance with Finnish Patent No. 89728 by the sameinventor and fed back to the process through air separating pumps 72according to Finnish Patent Application No. 935853 by the same inventor.Surplus water is fed over a level box to fiber recovery 66.

[0085] Trimmings 30 and broke 31 falling down at the paper productionare brought over a wire guide roller 56 wherefrom they are dropped intothe couch pit 10 by a doctor blade 58. Dilution water for diluting couchmass is fed by a dilution water conduit 60, the amount of water beingcontrolled by a valve 62 controlled by a valve 62 controlled by a flowregulator 64 so that the amount of water is kept proportional inrelation to the amount of couch mass fed. The dilution water isfavorably filtered or clear water from fiber recovery 66. By selectingthe consistency of the diluted couch mass so that it corresponds to theconsistency of the fed fresh stock one achieves a situation in which thewater from the fiber recovery 66 in all conditions of operation issufficient for the dilution, no water reservoir being needed for thispurpose.

[0086] During normal operation the diluted couch mass is pumped by apump 54 to stock preparation 59. At a web break the amount of couch masswill increase and thus also the flow of dilution water, whereby at leasta part of the increased amount is fed to a broke container 68.Preferably this is done with a broke pump 55, while the pump 54 can bedimensioned for less flow. The discharge flow from the couch pit 10 isfavorably controlled so that the level in the couch pit is maintained,by a pump 54, constant up to a pre-defined maximum variable flow, whilethe broke pump 55 is started immediately when the capacity of said pump54 has been exceeded so that a pre-defined maximum level has beenexceeded, in which case the level control is taken over by the brokepump 55 until the maximum level has been recovered.

[0087] The invention has been described mainly as applied to papermaking and treatment of couch mass in connection thereto. The use of theinvention is, however, not restricted to this application, but it canalso be extended to many other situations. Thus, the invention can beutilized in production and returning of, e.g., chemical engineeringproducts, concrete, etc.

What is claimed is:
 1. Apparatus for processing a fluid mass comprising: a. an upwardly open vessel or trough for receiving a fluid mass which falls down into the vessel or trough; b. a mixing arrangement arranged in the vessel or trough, said mixing arrangement comprising horizontally arranged rotatable cylinder means provided with spiral means and a discharge for processed mass, the cylinder means comprising at least tow cylinders arranged for rotation counter to each other; wherein c. each respective spiral means extends immediately from the surface of a cylinder core of the cylinder means in a direction towards a wall portion of the vessel or trough to the vicinity of the wall portion; d. cylinder means being arranged in a parallel disposition whereby the spiral means intermesh at least in pairs; e. first channels defined at said cylinder means, by a core surface of said cylinder means, an opposite wall section of the vessel or trough and adjacent ones of the spiral means provided at the cylinder and wherein; f. further channels including constrictions are defined by the intermeshing spiral means; g. which further channels extend in an inclined horizontal manner and have a smaller cross section than the cross section of the first channels.
 2. The apparatus according to claim 1 wherein the direction of rotation for each cylinder is such that the mass at least at the outermost cylinders is forced by said spiral means against the side walls of the vessel or trough and down along the side walls of the vessel or trough towards a semi-circular portion of the vessel or trough and, respectively against gable walls of the vessel or trough; wherein the dimensions of the discharge and of inlets are such that the mass, due to the oration of the spiral means, is at least partially forced through the channels in a direction away from the discharge such that a spiral system comprising the spiral means is so tight that pressure will be built up in front of the discharge.
 3. The apparatus according to claim 1 wherein each one of said cylinders provided with spiral means comprises a core in the shape of a displacement body having a diameter which is at least 50% of the total diameter of one of the cylinders, wherein more than one spiral is arranged at each cylinder; and the spirals are arranged in such a manner that their pitch is more than three diameters for each turn, and the angle α between the outer edge of the spiral and a normal plane perpendicular to the axis of the cylinder is in the range of more than 45° to more than 60°.
 4. The apparatus according to claim 3 wherein the diameter of the core is from 75 to 90% of the diameter of a spiral cylinder.
 5. The apparatus according to claim 3 wherein the angle a is from 65° to 85°.
 6. The apparatus according to claim 3 wherein the number of spirals at each cylinder is in the range of from 4 to
 40. 7. The apparatus according to claim 1 wherein the spiral means are arranged around the cylinder core along substantially the entire horizontal extent thereof.
 8. The apparatus according to claim 1 wherein the cylinders are arranged in pairs and are rotatable in such a manner that they form, at their outer side directed toward the wall of the vessel or trough together with the wall, a nip or wedge shaped inlet for the mass, such that each nip or each wedge shaped portion comprising the wedge shaped inlets comprises a shearing/cutting edge portion which co-acts with an edge of the spiral.
 9. The apparatus according to claim 8 wherein the nip or wedge shaped portion is formed also at an area between adjacent other pairs of cylinders.
 10. The apparatus according to claim 1 wherein the spirals are displacing spirals having a tight fit such that the spirals, at adjacent spirals working in an intermeshing manner, momentarily fill the space between the cores of the cylinders.
 11. The apparatus according to claim 1 wherein more than two cylinders provided with spirals are arranged in pairs for co-action.
 12. The apparatus according to claim 1 wherein there is more than one discharge, and the cylinders are each provided with spirals divided intro sections leading to a discharge.
 13. The apparatus according to claim 1 wherein the discharge is centrally arranged within the couch pit, and the spirals are divided into sections leading to a central portion of eth arrangement.
 14. The apparatus according to claim 1 wherein the discharge is located centrally between the co-acting pair of cylinders.
 15. The apparatus according to claim 1 wherein the sides and optionally also the bottom of the vessel or trough have a circumference and wherein the sides and optionally the bottom of the vessel or trough are designed to follow at least a portion of the circumference close to the periphery of the cylinders provided with the spirals.
 16. The apparatus according to claim 1 wherein the vessel or trough including the cylinders and the bottom of the vessel or trough is arranged to slope towards each discharge at a slope angle of from 1 to 5%, such that the cylinders and the spiral means share a corresponding conicity.
 17. A method for making paper, producing chemical engineering products, or producing concrete comprising introducing raw ingredients into an apparatus according to claim
 1. 18. A method for treating a fluid mass comprising feeding a mass material to a vessel or trough having a mixing device; said mixing device comprising rotatably arranged processing means; wherein at least two of said processing means are caused to rotate in opposite direction and substantially horizontally adjacent to one another; the method further comprising conveying the mass at the upper surface of the means out towards the respective opposite portions of the vessel or the trough, wherein the opposite portions are delimited in the radial direction of the processing means; bringing the mass, using a plurality of spiral elements arranged in an inclined manner at a substantially cylindrical core of each respective processing means, into horizontal channels arranged in an inclined manner; which channels define the core, by opposite wall portions of respectively two adjacent spiral elements, and by wall portions of the vessel which are adjacent to the spiral elements; and bringing the mass towards a constriction formed by intermeshed spiral elements arranged respectively at each two of said processing means rotating in opposite directions while disposed adjacent to each other.
 19. The method according to claim 18 further including bringing a part of the mass to be forced towards at least one discharge arranged in the vessel or trough by controlling the rotation of the spiral elements, and, respectively, the pitch of the spiral elements around the core or by additionally controlling at least one of an inlet or outlet parameter for the vessel or trough, while forcing the rest of the mass under the impact of at least one gable wall of the vessel or trough or under the impact of spirals working counter to each other in an intermeshed manner, or under the impact of both at least one gable wall of the vessel and the spirals, through the channels and in a direction away from the discharge or over the upper surface of the processing means, or away from the discharge as well as over the upper surface of the processing means to be combined with an added feed of mass.
 20. A method for treating a fluid mass comprising introducing a mass and dilution water into a couch pit comprising a vessel or trough and a mixing arrangement, the method further including brining at least two substantially horizontally arranged spiral cylinders of the mixing arrangement to rotate in an intermeshed manner counter to each other, thereby conveying the mass by means of spirals arranged at the spiral cylinders, wherein the mass falls down into the couth pit from above; drawing the mass into channels, formed by adjacent spirals by cores of the cylinders and by a wall of the vessel or trough, whereby the mass is conveyed towards a constriction formed by the cylinder cores and the intermesh of the spirals, thus forcing a part of the mass against at least one discharge, while re-circulating a part of the mass in channels formed at the constrictions; and forcing surplus back through the channels.
 21. The method according to claim 20 further comprising controlling the amount of dilution water in accordance with the width of a paper web falling down, which paper web comprises a couch mass, to a consistency corresponding to the consistency of fresh stock in a paper making process.
 22. The method according to claim 21 wherein the mass is returned to a stock processor without prior thickening.
 23. The method according to claim 21 further comprising restricting an amount of couch mass returned to a predefined proportion of the total mass while feeding surplus mass to a collector tank so that the level in the couch pit is restricted at a change in a paper machine to a minimum by controlling the rotation of the spiral cylinders or by controlling a choke arranged at the discharge. 